diff --git a/base/special/acosf/lib/main.js b/base/special/acosf/lib/main.js
index fd5d20808..2812ca8a3 100644
--- a/base/special/acosf/lib/main.js
+++ b/base/special/acosf/lib/main.js
@@ -90,6 +90,7 @@ function acosf( x ) {
 	if ( isnanf( x ) ) {
 		return NaN;
 	}
+	x = float64ToFloat32( x );
 	if ( x < -1.0 || x > 1.0 ) {
 		return NaN;
 	}
@@ -99,7 +100,6 @@ function acosf( x ) {
 	if ( x === -1.0 ) {
 		return PI;
 	}
-	x = float64ToFloat32( x );
 	ax = absf( x );
 	if ( ax < 0.5 ) {
 		if ( ax <= SMALL ) {